The knee joint is a uni-axial hinge joint. The knee moves in a flexion (bending of the knee) and extension (straightening of the knee) direction. The three major bones that form the knee joint are: the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). The prime muscle movers of the knee joint are the quadriceps muscles (on top of the femur), which move the knee into extension; and the hamstring muscles (underneath the femur), which move the knee into flexion. The quadriceps muscles are made up of five muscles known as the rectus femoris, vastus lateralis, vastus medialis, vastus intermedius and a secondary muscle, the vastus medialis oblique (VMO). The hamstring is made up of three muscles known as the biceps femoris, semimembranosus, and semitendinosus. The hamstring to quadriceps muscle strength ratio is two-thirds; meaning, the hamstring should be approximately thirty-three percent weaker than the quadriceps. The muscles, ligaments, nervous system, and skeletal system work in unison to stabilize the knee during gait activities (walking, running, jumping).
The stability and integrity of the knee joint and supportive musculature are greatly affected by the nervous system (sensation-reaction) and edema (swelling). Even minimal amounts of pain and swelling are enough to alter the normal quadriceps-hamstring relationship, which decreases the knee joint's capability and integrity. When this relationship is compromised, one of three general scenarios is likely to result:
1. The person will be unable to perform at his or her previous physical level. Decreased performance levels will be evident and the possibility of tendonitis, sprains, and strains is increased.
2. The VMO/Quadriceps group will not operate at a level sufficient enough to prevent sudden buckling (collapsing) of the knee, risking injury to internal and external knee components.
3. The hamstring muscle group will not work at an efficient level to prevent hyperextension of the knee, risking injury through tearing internal knee components.
Common internal knee injuries include cartilage tears, meniscal tears, and ligamentous (ACL and PCL) tears. Common external knee injuries include muscular tears (hamstring, quadriceps, and gastro-nemius) and ligamentous tears (MCL and LCL). Most of the described injuries will cause loss of time from work and may require physical therapy and/or surgical intervention.
The Anterior Cruciate Ligament (ACL) is one of the most commonly injured knee ligaments with 250,000 injuries occurring each year, at a cost of approximately $100,000,000.00. For the patients who decide to undergo surgery and rehabilitation for an ACL injury, costs will exceed $4,000.00 in medical bills per injury. These costs do not include any durable medical equipment, which includes functional knee bracing, or lost time at work. Of these 250,000 injuries, seventy percent are non-contact injuries. There are three common ways to injure an ACL:                1. The most common occurrence of ACL injuries happens during deceleration of the body along with pivoting/cutting.        2. The ACL ruptures during knee hyperextension, as a result of decreased hamstring capabilities.        3. Movements and actions performed by the human body that are out of control, for which the knee is unable to adequately adjust, are common in combat.        
The average recovery time for an athlete from an ACL injury varies from six months to more than a year. In order to combat this, many football linemen are currently wearing knee-bracing systems as a preventative tool. However, females have been shown to have a greater chance of injury than their male counterparts by two to eight times. With the military looking at expanding the role of females in combat and non-combat situations, the potential rise in lost time of service may increase in the future. The post-surgical ACL patient will require a functional brace after injury.
Current commercially available knee bracing apparatuses on the market for ligament and cartilage injuries are passive support systems. They work by minimizing excessive motions in certain planes to help prevent possible injury. Though many braces attempt to minimize the potential of a hyperextension injury, these braces do not minimize the chance of a buckling injury. Commercially available passive knee braces do not adequately address the issues of trying to control swelling and pain during gait activities.
Various embodiments of the present invention pertain to knee braces which provide novel and non-obvious apparatus and methods for support of human knees, and also for replacement of human knees.